Printing system for anodized aluminum

ABSTRACT

AN INK SYSTEM FOR FOUR-COLOR (MULTICOLOR) PRINTING OF ANODIZED ALUMINUM BY GRAVURE TECHNIQUES COMPRISING USE IN THE INK SYSTEM OF A SPECIALLY SELECTED GROUP OF COLORANTS. THE COLORANTS WHICH INCLUDE ORASOL YELLOW, ORASOL SCARLET, ORACET BLUE B, ORASOL RED, AVIATION OIL BLUE, LATYL CERISE B, SUDAN YELLOW, FLUOROL 7 BA, GRASOL BLUE AND NEOZAPON BLUE, ARE EACH ADAPTED TO COOPERATE WITH EACH OTHER IN MATTERS OF PENETRATION OF THE ANODIC FILM ON ALUMINUM, IN REASONABLY EQUIVALENT RESISTANCE TO THE FADING EFFECTS OF LIGHT AND IN OTHER RESPECTS PECULIAR TO THE SUCCESSFUL MULTICOLOR PRINTING OF ANODIZED ALUMINUM.

United States Patent 3,558,446 PRINTING SYSTEM FOR ANODIZED ALUMINUMCarl B. Blake, Bronx, and Adolph Fuerst, Brooklyn, N.Y., assignors toMartin Marietta Corporation, New York, N.Y., a corporation of MarylandNo Drawing. Filed June 28, 1968, Ser. No. 740,852 Int. Cl. B41m 1/10,1/14; C23f 17/00 U.S. Cl. 204-38 5 Claims ABSTRACT OF THE DISCLOSURE Thepresent invention is directed to printing anodized aluminum, and moreparticularly, to four-color printing of anodized aluminum by gravureprinting techniques.

For design purposes, it is desired to print anodized aluminum with highquality prints in full color. Heretofore, from the practical point ofView, printing of anodized aluminum in full color has been limited toprinting by silk screen methods which, in general, do not produce a highquality print job. Silk screen prints involve the deposit of a thicklayer of ink, show the mesh pattern on print edges and, in general, arenot adapted to reproduce fine detail. Other processes, such as gravureprinting, are capable of producing a high quality print, but heretoforehave not been adapted to print anodized aluminum in full color on acommercial scale. It is only relatively recently that the anodizing arthas developed from essentially batch operation to coil line anodizingwhere gravure presses can be used with advantage. Consequently, the arthas not developed the ink technology necessary to print on anodizedaluminum with the speed and precision now possible.

It has now been discovered that, by means of a novel system of inks,high quality full color printing by gravure means can be achieved onanodized aluminum surfaces.

It is an object of the present invention to provide an ink systemadapted for use in gravure printing of anodized aluminum.

It is another object of the present invention to provide a novel gravureprocess for printing anodized aluminum.

Other objects and advantages of the present invention will becomeapparent from the following description:

Generally speaking, the present invention contemplates an ink systemcomprising four inks, a black, a magenta, a yellow and a cyan, eachcontaining gravure type varnish having a viscosity of about 100 to about250 centipoises and having dispersed or dissolved therein one or more ofthe colorants selected from the group consisting of Orasol Yellow GRLN,Orasol Scarlet BB, Oracet Blue B, Orasol Red 2B, Aviation Oil Blue,Latyl Cerise B crude ground, Sudan Yellow GRA Conc., Fluorol 7GA, GrasolBlue LS, and Neozapon Blue FLE. The process of the present inventioncomprises anodizing aluminum or an alloy rich in aluminum in an aqueouselectrolyte to provide a porous anodic film thereon, drying said porousanodic film, depositing the aforesaid ink system from a quadruplicity ofgravure plates onto said anodized surface, each of said quadruplicity ofgravure plates carrying only one ink in one color from the group ofcyan, magenta, yellow and black, rapidly drying the ink deposits,sealing the thus printed and dried anodized surface by a methodcompatible with all of the colorants of the system, and removing fromsaid sealed surface any excess resin or colorant which may be present Asis well known in the art, aluminum, including alloys rich in aluminum,can be anodized in an aqueous electrolyte to produce a porous anodicsurface, which porous anodic surface is adapted to be sealed by means ofhot or boiling water. One of the most common methods of anodizing is tomake the object to be anodized the anode in an aqueous bath containingabout 15% by weight sulphuric acid and pass a unidirectional electriccurrent through the bath to anodize the aluminum object at an anodiccurrent density of about 10-15 amperes per square foot while maintainingthe anodizing bath at a temperature of about 25 C. If the electrolyte isat a temperature much above about 25 C., the anodized coating will betoo porous and will not seal properly. If the electrolyte is too cold,the anodized coating will tend to be non-porous and will not acceptcolorant. The thickness of the anodic layer produced is generally timedependent up to thicknesses of approximately 0.7 mil. Anodic coatingsthicker than about 0.7 mil require long anodizing times to produce andare not commonly employed in processes concerned with decoration ofaluminum. Thicknesses of anodic film which can be satisfactorily printedin accordance with the process of the present invention, e.g. about 0.1to about 0.7 mil, can be achieved by anodizing from 10 to about 40minutes at the aforestated anodic current density. By using higheranodic current densities, it is possible to cut down the anodizing timeto times of about 5 minutes but care must be taken to avoid overheatingthe electrolyte and consequent weakening of the anodic film. As will beobvious to those skilled in the art, equivalent porous anodic films canbe produced by other known aluminum anodizing means. As a caution,however, it is suggested that anodizing in chromate solution be avoidedunless, for one reason or another, it is desired to print on a surfacehaving a yellowish tinge.

As mentioned hereinbefore, the ink system of the pres ent inventionemploys a gravure type varnish. Such a varnish must be of relatively lowviscosity in order to adequately fill the cells of a gravure plate, beproperly doctored and be deposited on the print-receiving surface at thetime of contact between the plate and the printreceiving surface. Agravure type varnish having as a binder a mixture of medium molecularweight ethyl cellulose and gum rosin in a ratio of 2 to about 3 parts ofethyl cellulose to one part of gum rosin, said binder being dissolved ina combination of ester, alcohol and ketonic solvents, has been found tobe quite satisfactory. Other gravure type varnishes are also operativein the present invention. Varnishes can include other polymers such asethyl hydroxyethyl cellulose and nitrocellulose in place of ethylcellulose in admixture with gum rosin or other grades of rosin in amutually compatible solvent or solvent mixture. The ratio of polymer torosin set forth above is necessary in order to maintain a proper balancebetween film integrity and ease of cleaning the aluminum surface aftersealing.

A specific list of colorants identified by the commercial names has beendisclosed hereinbefore as suitable for use in the present invention.These colorants are also set forth in Table I along with their ColourIndex designation where such is known.

Latyl Cerise B crude ground Sudan Yellow GRA coneent G. Yellow 30,Fluorol TGA t G. Yellow 43. Grasol Blue LS Gy Blue Noozapon Blue FLEBASF...

ClBA=Ciba Chemical and Dye 00., Div. of Ciba Corp; CCC= AmericanCyanamid 00., Dyes dept.; DuP=E. I. du Pont de Nemours & 00., 1110.; GGeneral Aniline & Film Corp.; Gy=Geigy Chem. Corp BASF=Badiscl1e Anilin& Soda Fabriken.

Z Disperse.

The selection of the colorants set forth in Table I is not arbitrary. Itmust be recognized that in order for a four-color system of gravureprinting on anodized aluminum to be operable, the colorants and inksmust not only have the well-known color characteristics common to allprocess printing, but must be chemically and physically adapted tocooperate in the printing, sealing, and decorative aspects of theprocess. The colorants used must be reasonably equal in absorptioncharacteristics with respect to anodized aluminum. Contrary to printingon paper or other porous substrates, the print deposit on anodizedaluminum does not uniformly enter the pores of the anodized aluminum.The pores in unsealed anodized aluminum are ultramicroscopic indimension. Binder molecules, such as ethyl cellulose, are too large toenter the pores. Thus the printed deposit as a Whole does not enter theanodized aluminum pores and consequently the migratory characteristicsof the colorants used in the ink system into the pores must bereasonably equal. More important the colorants in later deposited inksmust migrate readily through previously deposited ink in order toachieve the process printing effect of an unlimited number of colors inthe anodized layer on the aluminum. As a second point critical to theprinting of anodizing aluminum, the colorants used must be equallyadapted to refrain from bleeding or otherwise discoloring in the sealingprocess. For example, if one were to use a black ink made up with red,yellow and blue colorants wherein the yellow and blue colorants are fastin water sealing, but the red colorant bleeds into the sealing bath, theultimate printing result on the sealed anodized aluminum would be agreenish-black color surrounded by a red halo or, in an extreme case, areddish background color. It is obvious that such a print would becommercially unsatisfactory. A third characteristic which must be commonto the colorants used in the printing of anodized aluminum issubstantially equal light fastness. Unlike an illustration on the insideof a book, which is normally not exposed to light for any substantialperiod of time, or a magazine cover which has only a limited usefulcommercial lifetime, a decorated, anodized aluminum object is designedto be exposed to light, perhaps continuously, and must have asubstantial useful commercial lifetime measured in terms of years underordinary artificial illumination. As an example, if a four-colordecorated anodized aluminum object, for example a refrigerator door, isplaced in service and, after a relatively short period of time, e.g.several months, one of the colorants fades more than another of thecolorants, the result is an off-color object which is commerciallyunsatisfactory. As of the present time, there is no sure cure for fadingof color upon exposure to light. However, if, as in the colorcombinations of the present invention, the colors fade reasonablyuniformly, then the color tone of the anodized aluminum object willremain reasonably constant even though the color intensity may very welldiminish with time. Thus, while it is very pos- Sible for one to selectfrom colorants available to the art, many examples of magenta, yellow,cyan, black colorants, these other readily available colorants are notthe equivalents of the colorants set forth in Table I for purposes ofthe present invention. As a good example of what is meant by theforegoing, it is pointed out that in most process printing on substratesother than anodized aluminum, a printer usually uses a blue (cyan) inkcontaining Monastral Blue (copper phthalocyanine) as a pigment.Monastral Blue colorant is recognized universally as a pigment of highcolor intensity and very great resistance to fading by light, oxidation,etc. Nevertheless, for purposes of the present invention, Monastral Blueis completely useless since its pigmentary form will not allow it tomigrate into the ultra-microscopic anodized aluminum pores.

The colorants set forth in Table I are specifically adapted to beemployed in connection with a water sealing process. For purposes ofthis specification and claims, water sealing process includes not onlysealing in boiling aqueous media, but also sealing with steam and withdilute aqueous solutions of hydrolyzable salts, e.g. cobalt or nickelacetate, at temperatures above about 90 F. Normally water sealing iscarried out in the same manner as is common to the anodized aluminumart. For example, in boiling water, sealing can be conducted for about20 minutes, whereas if an anodized aluminum object is sealed in a 2%cobalt or nickel acetate solution at 195 F., sealing will probably besatisfactorily completed in 5-10 minutes.

For the purpose of giving those skilled in the art a betterunderstanding of the invention, the following example of an ink systemin accordance with the present invention is given. A varnish is made bydissolving 15 parts by weight of ethyl cellulose (grade N4) and 5 partsby weight of gum rosin in parts by weight of a mixture of butyl acetate,isopropylacetate, ethyl alcohol, butyl Cellosolve and methyl isobutylketone. Process color inks were made from this varnish as follows:

A black ink was made by dispersing about 10 parts of Orasol Yellow GRLN,7 parts of Orasol Scarlet BB and 15.5 parts of Oracet Blue B in about 70parts by weight of the varnish. A yellow process ink was made bydispersing about 14-15 parts by weight of Orasol Yellow GRLN, in about86 to parts by weight of varnish. A magenta ink was made by dispersingabout 7 parts by weight of Orasol Red 2B and 93 parts by weight varnish.A cyan ink was made by dispersing about 14-15 parts by weight ofAviation Oil Blue in about 85 parts by weight of varnish. An aluminumsurface was anodized to a thickness of about 0.5 mil, was rinsed anddried. The anodized aluminum surface was process printed from thegravure plates using the aforedescribed black, yellow, magenta and cyaninks which, just prior to printing, were cut 1:1 in parts by weight withbutyl acetate in order to reduce the viscosity thereof. The solvents inthe completed print were allowed to evaporate and the completed printwas then sealed in boiling water for 25 minutes. The result was a veryhigh quality print having excellent color intensity and substantiallyuniform resistance to fading.

While the present invention has been described in conjunction withadvantageous embodiments, those skilled in the art will recognize thatmodifications and variations may be resorted to without departing fromthe spirit and scope of the invention. Such modifications and variationsare considered to be within the purview and scope of the invention.

We claim:

1. A process of printing anodized aluminum in multicolor comprisingdepositing in sequence from a quadruplicity of gravure plates amulti-color image onto a porous anodized aluminum substrate, said imagebeing comprised of a yellow image, a magenta image, a cyan image and ablack image, sealing said porous surface containing the thus depositedimage, and cleaning any excess of said multi-color image from the thussealed anodized aluminum surface, said yellow image comprising a gravureink containing a colorant selected from the group consisting of OrasolYellow GRLN, Solvent Yellow 30 and Solvent Yellow 43, said magenta imagecomprising a gravure ink containing a colorant selected from the groupconsisting of Solvent Red 50', Solvent Red 9 and Disperse Red 59, saidcyan image, comprising a gravure ink containing a colorant selected fromthe group consisting of Solvent Blue 19, Solvent Blue 58, and SolventBlue 55 and said black ink comprising a gravure ink containing ascolorants at least one colorant from each group of colorants in the inkscomprising the yellow, magenta and cyan images.

2. A process as in claim 1 wherein the porous anodized aluminumsubstrate is fed through a printing station containing each of thequadruplicity of gravure plates as cylinders in mutual register.

3. A process as in claim 1 wherein the porous anodized 15 aluminum issealed in an aqueous medium.

4. A process as in claim 1 wherein the gravure inks also contain aresinous polymer and rosin, in a ratio of about 2 to about 3 parts ofresinous polymer to one part of rosin, dissolved in solvent therefor.

6 5. A process as in claim 1 wherein the porous anodized aluminumpossesses an anodic surface prepared by anodizing aluminum at about roomtemperature in an aqueous bath containing about 15% sulfuric acid byweight.

References Cited UNITED STATES PATENTS 172,892 2/1876 Smith 1014262,772,630 12/1956 Share 101426UX 2,989,917 6/1961 Brodie 1012113,049,077 8/1962 Damm, Jr 101211 3,079,309 2/ 1963 Wainer 204-3 8X3,193,416 7/1965 Michelson 20438X 3,290,232 12/1966 Dunning 204-35ROBERT E. PULFREY, Primary Examiner C. D. CROWDER, Assistant ExaminerUS. Cl. X.R.

Patent No. ,446 Dated January 26, 1971 Inventor) Carl B. Blake andAdolph Fuerst It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 3, Table I, last column Colour index designation, solvent shouldbe Colour Index Designatio Red 50. Solvent Red 50 Blue 19. Solvent Blue19 Red 9. Solvent Red 9 Blue 58. Solvent Blue 58 Red 59. 2 Disperse Red59 Yellow 30. Solvent Yellow 30 Yellow 43. Solvent Yellow 43 Blue 19.Solvent Blue 19 Blue 55. Solvent Blue 55 Disperse.

Signed and sealed this 15th day of June 1971.

(SEAL) Attest:

EDWARD M.FIETCHER,JR. WILLIAM E. SGHUYLER, Attesting OfficerCommissioner of Pate] I-A-U A tall (In an l. ,1..

